Process for producing high quality pyrolysis oil from biomass

ABSTRACT

This invention relates to a process to utilize a torrefaction pretreatment step for biomass pyrolysis process. This pretreatment improves the quality of the pyrolysis oil by reducing acidity. The inventive process shows that as a pretreatment to pyrolysis, resulting pyrolysis oil obtained from torrefied biomass has approximately 25% lower acetic acid than that from untorrefied biomass pyrolysis oil.

CROSS-REFERENCE TO RELATED APPLICATIONS

None.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

None.

FIELD OF THE INVENTION

The present invention relates generally to the conversion of biomass tofuel range hydrocarbons.

BACKGROUND OF THE INVENTION

Due to governmental legislation as mandated in the Renewable FuelsStandards (RFS), the use of renewable energy sources is becomingincreasingly necessary to reduce emissions of carbon based fuels andprovide alternatives to petroleum based energy and feedstock. One of thealternatives being explored is the use of biomass. Biomass is any carboncontaining material derived from living or formerly living organisms,such as wood, wood waste, crops, crop waste, waste, and animal waste.

Pyrolysis is the chemical decomposition of organic materials by heatingin the absence of oxygen or other reagents. Pyrolysis can be used toconvert biomass (such as lignocellulosic biomass) into pyrolysis oil orso-called bio-oil. The bio-oils obtained by pyrolysis of biomass orwaste have received attention recently as an alternative source of fuel.

Generally the pyrolysis of biomass produces four primary products,namely water, “bio-oil,” also known as “pyrolysis oil,” char, andvarious gases (H₂, CO, CO₂, CH₄, and other light hydrocarbons) that donot condense, except under extreme conditions. For exemplary purposes,the pyrolysis decomposition products of wood from white spruce andpoplar trees are shown in Table 1.

TABLE 1 Source: Piskorz, J., et al. In Pyrolysis Oils from Biomass,Soltes, E. J. Milne, T. A., White Eds., ACS Symposium Series 376, 1988.Spruce Poplar Moisture content, wt % 7.0 3.3 Particle size, μm (max)1000 590 Temperature 500 497 Apparent residence time 0.65 0.48 ProductYields, wt %, m.f. Water 11.6 12.2 Gas 7.8 10.8 Bio-char 12.2 7.7Bio-oil 66.5 65.7 Bio-oil composition, wt %, m.f. Saccharides 3.3 2.4Anhydrosugars 6.5 6.8 Aldehydes 10.1 14.0 Furans 0.35 — Ketones 1.24 1.4Alcohols 2.0 1.2 Carboxylic acids 11.0 8.5 Water-Soluble - Total Above34.5 34.3 Pyrolytic Lignin 20.6 16.2 Unaccounted fraction 11.4 15.2

Fast pyrolysis is one method for the conversion of biomass to bio-oil.Fast pyrolysis is the rapid thermal decomposition of organic compoundsin the absence of atmospheric or added oxygen to produce liquids, char,and gas. Fast pyrolysis affords operation at atmospheric pressure,moderate temperatures, and with low or no water usage. Pyrolysis oilyields typically range from 50-75% mass of input biomass and are heavilyfeedstock dependent.

The major advantage of these fuels is that these are CO₂ neutral andcontain a very low fraction of bonded sulfur and nitrogen. Thus, theycontribute very little to the emission of greenhouse gases or otherregulated air pollutants.

There has been a considerable effort in the past to develop pyrolysisprocesses for the conversion of biomass and waste to liquids for theexpress purpose of producing renewable liquid fuels suitable for use inboilers, gas turbines and diesel engines.

However, pyrolysis oil obtained from biomass fast pyrolysis process ischemical complex compounds comprising generally a mixture of water,light volatiles, and non-volatiles. They are in general of relativelylow quality. As fuels they have a number of negative properties such ashigh acidity (lead to corrosion problem), substantial water content(usually in the range of 15% to 30%), variable viscosity, low heatingvalues (about half that of the diesel fuel), low cetane number, etc.These negative properties are related to the oxygenated compoundscontained in bio-oils that result in a 45% oxygen content. In general,the pyrolysis oil has total acidity number (TAN) value of approximately100. The desired TAN value for transportation fuel is less than 10.

There has been a considerable effort in the past to address the high TANproblem by post treatment or upgrading the pyrolysis oils before theyare used as a regular fuel. Most method essentially involves the removalof oxygen. Particular attention has been focused on hydrotreating usingconventional petroleum catalysts, for example, cobalt-molybdenum ornickel-molybdenum on alumina to produce essentially oxygen-freenaphthas. Since pyrolysis liquids typically contain between 30 to 50 wt% of oxygen, complete removal of oxygen requires a substantialconsumption of hydrogen which represents a major and prohibitive cost.

Therefore, developing a new method or process for improving quality ofpyrolysis oil would be a significant contribution to the art.

BRIEF SUMMARY OF THE DISCLOSURE

Generally speaking, this invention discloses a process for producinghigh quality pyrolysis oil from biomass by utilizing a torrefactionpretreatment step for biomass pyrolysis process wherein the pretreatmentstep improves the quality of the pyrolysis oil by reducing acidity.

The disclosed process comprises at least the following steps: a) a stepof subjecting a biomass feedstock to a thermal treatment in a reactor Aunder a torrefaction reaction condition to produce an torrefied biomassfeedstock; and b) a step of pyrolyzing the torrefied biomass feedstockin a reactor B under a pyrolysis reaction condition to form a pyrolysisoil product.

The torrefaction reaction condition includes a temperature ranging from180° C. to 350° C., a pressure ranging from atmospheric pressure to 500psia, and a residence time ranging from 1 minute to 24 hours. Thepyrolysis reaction condition includes a temperature ranging from 375° C.to 700° C., a pressure ranging from vacuum conditions (0.1 psia) to 1000psia., and a residence time ranging from 0.1 to 200 seconds. Thepyrolysis oil product according to the current invention has a TANnumber between 80 and 200.

BRIEF DESCRIPTION OF THE DRAWINGS

None.

DETAILED DESCRIPTION

Embodiments of the invention relate to a process to utilize atorrefaction pretreatment step for biomass pyrolysis process. Thispretreatment improves the quality of the pyrolysis oil by reducingacidity. The inventive process shows that as a pretreatment topyrolysis, resulting pyrolysis oil obtained from torrefied biomass hasapproximately 25% lower acetic acid than that from untorrefied biomasspyrolysis oil.

As used herein, the term “biomass” includes any renewable source (livingor formerly living), but does not include oil, natural gas, and/orpetroleum. Biomass thus includes but is not limited to wood, paper,crops, animal and plant fats, biological waste, algae, and the like.

According to one embodiment of the invention, there is disclosed a stepof subjecting a biomass feedstock to a thermal treatment in a reactorunder a torrefaction reaction condition to produce a torrefied biomassfeedstock.

Torrefaction consists of a slow heating of biomass feedstock in an inertatmosphere to produce a solid with lower hemicellulose content, higherenergy density, nearly moisture free (<3 wt %), and low resistance tofracture (brittle).

Any standard torrefaction reactor can be used to torrefy the biomassfeedstock. Exemplary reactor configurations include without limitationsaugers reactor, ablative reactor, rotating cones reactor, fluidized-bedreactor, entrained-flow reactor, vacuum moving-bed reactor,transported-bed reactor, and fixed-bed reactor.

Any standard torrefaction reaction condition can be used to torrefy thebiomass feedstock in the torrefaction reactor. A person skilled in theart can readily select a combination of temperature, pressure, andresidence time that produces a torrefied product. In one embodiment, thetorrefaction reaction condition includes a temperature ranging from 180°C. to 350° C., a pressure ranging from atmospheric pressure to 500 psia,and a residence time ranging from 1 minute to 24 hours. In anotherembodiment, the torrefaction reaction condition includes a temperatureranging from 220° C. to 280° C., a pressure ranging from 11 psia to 30psia, and a residence time ranging from 5 to 20 minutes. In yet anotheralternative embodiment, the torrefaction reaction conditions include atemperature ranging from 180° C. to 350° C., a pressure ranging from 0.1psia to 500 psia, and a residence time ranging from 1 minute to 24hours.

A variety of catalysts may be used for torrefaction reaction. In someembodiments, torrefaction is carried out in the presence of a catalystmaterial selected from a group consisting solid acid catalyst such asZSM5, solid base catalyst such as Hydrotalcite, silica catalyst such asDiatomite, silica-alumina catalyst such as Kaolin, Group B metal oxidecatalyst such as Ammonium Molybdate, pyrolytic char and any combinationthereof.

In some embodiments, the torrefaction reaction is carried out in theabsence of diatomic oxygen in an inert gas atmosphere such as nitrogen,argon, steam, carbon oxides, etc. In some embodiments, the torrefactionreaction is carried out in a reducing gas atmosphere that comprisescarbon monoxide. Also, torrefaction may be carried out with otherreactants such as hydrogen, ammonia, etc.

The torrefied biomass according to various embodiments of the inventionmay be added to a pyrolysis reactor for further processing. In someembodiments, the torrefied biomass is pyrolyzed in a pyrolysis reactorunder pyrolysis reaction conditions to form a pyrolysis oil product.

Pyrolysis, which is the thermal decomposition of a substance into itselemental components and/or smaller molecules, is used in variousmethods developed for producing hydrocarbons, including but not limitedto hydrocarbon fuels, from biomass. Pyrolysis requires moderatetemperatures, generally greater than about 325° C., such that the feedmaterial is sufficiently decomposed to produce products which may beused as hydrocarbon building blocks.

Embodiments of the inventive process use any standard pyrolysis reactorproviding sufficient heat to pyrolyze torrefied biomass feedstock,including without limitation, auger reactor, ablative reactor, abubbling fluidized bed reactor, circulating fluidized beds/transportreactor, rotating cone pyrolyzer, vacuum pyrolyzer, and the like.

Any standard pyrolysis reaction condition can be used to pyrolyze thetorrefied biomass feedstock in a pyrolysis reactor. A person skilled inthe art can readily select a combination of temperature, pressure, andresidence time that produces a pyrolyzed product. In one embodiment, thepyrolysis reaction condition includes a temperature ranging from 375° C.to 700° C., a pressure ranging from vacuum condition to 1000 psig., anda residence time ranging from 0.1 to 200 seconds. In another embodiment,the pyrolysis reaction condition includes a temperature ranging from425° C. to 525° C., a pressure ranging from atmospheric pressure to 300psia., and a residence time ranging from 0.5 to 2 seconds.

A variety of catalysts may be used for the pyrolysis reaction. In oneembodiment, the pyrolysis reaction is carried out in the presence of acatalyst material selected from a group consisting of solid acidcatalyst such as ZSM5, solid base catalyst such as Hydrotalcite, silicacatalyst such as Diatomite, silica-alumina catalyst such as Kaolin,Group B metal oxide catalyst such as Ammonium Molybdate, pyrolytic charand any combination thereof.

The pyrolysis oil product obtained according to some embodiments of thepresent invention has a TAN number between 80 and 200. The pyrolysis oilproduct obtained according to some other embodiments of the presentinvention has a TAN number between less than 20 and 50.

The following examples of certain embodiments of the invention aregiven. Each example is provided by way of explanation of the invention,one of many embodiments of the invention, and the following examplesshould not be read to limit, or define, the scope of the invention.

Example 1

The comparison study of the process of torrefaction prior to pyrolysishas been performed in a micropyrolysis unit. The reactions were carriedout at torrefaction temperatures ranging from 179° C. to 321° C. andpyrolysis temperatures ranging from 379° C. to 521° C. with no catalystloading. In addition, a wide variety of biomass was tested including redoak, switchgrass, miscanthus, and corn stover pellets. Comparativepyrolysis tests were run without the torrefaction pretreatment at thesame pyrolysis temperatures.

Results:

The experimental results indicating the reduction of acetic acid in thepyrolysis product due to torrefaction are shown as follows:

TABLE I Average Acetic Acid Yield. Torrefaction- Pyrolysis PyrolysisReduction³ Yield¹, Yield¹, Conc.², Yield¹, Conc.², Biomass wt-% Conc.²,% wt-% % wt-% % Oak 8.76 5.38 6.29 4.40 28.2 18.1 Switchgrass 4.64 4.793.07 3.96 34.0 17.3 Miscanthus 3.75 6.25 2.35 4.41 37.2 29.4 Corn Stover1.89 5.41 0.74 3.29 60.7 39.3 ¹Mass of acetic acid over mass of biomass²Acetic acid peak area over total peak area by GC/MS³Torrefaction-pyrolysis acetic acid level relative to pyrolysis aceticacid level

The result above shows that the acetic acid concentration in pyrolysisoil products was reduced by 18 to 39% with this pretreatment than thatfrom un-torrefied biomass. The resulting pyrolysis oil would have asimilar reduction in TAN (total acid number) value as ˜80% of the TAN isdue to acetic acid in pyrolysis oils.

Discussion:

As discussed above, the pyrolysis oil obtained from biomass fastpyrolysis process is of relatively low quality. In general, pyrolysisoil has TAN value of approximately 100. The desired TAN value fortransportation fuel is less than 10.

The results above shows that using torrefied biomass as a pretreatedfeed for pyrolysis helps reduce TAN (total acid number) of the pyrolysisoil product. The pretreatment by torrefaction according to the currentinvention helps to significantly reduce the TAN value of the pyrolysisoil product by 25%. This is mainly attributed to the release of aceticacid in the torrefaction step.

The step of pretreatment of torrefaction can be easily integrated withthe pyrolysis step. The pretreatment step improves the quality of thefeed quality of pyrolysis step and therefore results in higher qualityof pyrolysis oil product including low TAN value. In addition, suchintegrated process reduces the operating cost and capital investment ofpost treatment process.

It should be noted that, as used in this specification and the appendedclaims, the singular forms “a,” “an,” and “the” include pluralreferences unless the content clearly dictates otherwise. Thus, forexample, reference to a composition containing “a compound” includes amixture of two or more compounds. It should also be noted that the term“or” is generally employed in its sense including “and/or” unless thecontent clearly dictates otherwise. It should also be noted that, asused in this specification and the appended claims, the phrase“configured” describes a system, apparatus, or other structure that isconstructed or configured to perform a particular task or adopt aparticular configuration. The phrase “configured” can be usedinterchangeably with other similar phrases such as arranged andconfigured, constructed and arranged, constructed, manufactured andarranged, and the like.

Although the systems and processes described herein have been describedin detail, it should be understood that various changes, substitutions,and alterations can be made without departing from the spirit and scopeof the invention as defined by the following claims. Those skilled inthe art may be able to study the preferred embodiments and identifyother ways to practice the invention that are not exactly as describedherein. It is the intent of the inventors that variations andequivalents of the invention are within the scope of the claims, whilethe description, abstract and drawings are not to be used to limit thescope of the invention. The invention is specifically intended to be asbroad as the claims below and their equivalents. In closing, it shouldbe noted that each and every claim below is hereby incorporated intothis detailed description or specification as an additional embodimentsof the present invention.

1. A process for producing pyrolysis oil product from biomass comprisingat least the following steps: a) a step of subjecting a biomassfeedstock to a thermal treatment in a reactor A under a torrefactionreaction condition to produce an torrefied biomass feedstock; b) a stepof pyrolyzing said torrefied biomass feedstock in a reactor B under apyrolysis reaction condition to form a pyrolysis oil product, whereinsaid torrefaction reaction conditions includes a temperature rangingfrom 180° C. to 350° C., a pressure ranging from 11 psia to 500 psia,and a residence time ranging from 1 minute to 24 hours, wherein saidpyrolysis reaction conditions includes a temperature ranging from 375°C. to 700° C., a pressure ranging from 0.1 psia to 1000 psia, and aresidence time ranging from 0.1 to 200 second, and wherein saidpyrolysis oil product has a TAN number between 80 and
 200. 2. Theprocess of claim 1, wherein said torrefaction reaction conditionsincludes a temperature ranging from 220° C. to 280° C., a pressureranging from 11 psia to 30 psia, and a residence time ranging from 5 to20 minutes, wherein said pyrolysis reaction conditions includes atemperature ranging from 425° C. to 525° C., a pressure ranging fromatmospheric pressure to 300 psia., and a residence time ranging from 0.5to 2 seconds, and wherein said pyrolysis oil product has a TAN numberbetween 20 and
 50. 3. The process either claim 1 or 2, wherein saidtorrefaction reaction is carried out in said reactor A selected from agroup consisting of an augers reactor, an ablative reactor, a rotatingcones reactor, a fluidized-bed reactor, an entrained-flow reactor, avacuum moving-bed reactor, a transported-bed reactor, and a fixed-bedreactor.
 4. The process either claim 1 or 2, wherein said pyrolysisreaction is carried out in said reactor B selected from a groupconsisting of an auger reactor, an ablative reactor, a bubblingfluidized bed reactor, a circulating fluidized bed/transport reactor, arotating cone pyrolyzer, and a vacuum pyrolyzer.
 5. The process eitherclaim 1 or 2, wherein said torrefaction reaction is carried out in thepresence of a catalytic material selected from a group consisting acidcatalysts, solid base catalysts, silica catalysts, silica-aluminacatalysts, Group B metal oxide catalysts, pyrolytic char and anycombination thereof.
 6. The process either claim 1 or 2, wherein saidtorrefaction reaction is carried out in the presence of a catalyticmaterial selected from a group consisting ZSM5, Hydrotalcite, Diatomite,Kaolin, Ammonium Molybdate, pyrolytic char and any combination thereof.7. The process either claim 1 or 2, wherein said pyrolysis reaction iscarried out in the presence of a catalytic material selected from agroup consisting acid catalyst, solid base catalyst, silica catalyst,silica-alumina catalyst, Group B metal oxide catalyst, pyrolytic charand any combination thereof.
 8. The process either claim 1 or 2, whereinsaid pyrolysis reaction is carried out in the presence of a catalyticmaterial selected from a group consisting ZSM5, Hydrotalcite, Diatomite,Kaolin, Ammonium Molybdate, pyrolytic char and any combination thereof.9. The process of either claim 1 or 2, wherein said torrefactionreaction is carried out in the absence of diatomic oxygen in an inertgas atmosphere comprising nitrogen, argon, steam or carbon oxide. 10.The process of either claim 1 or 2, wherein said torrefaction reactionis carried out in a reducing gas atmosphere.
 11. The process of claim10, wherein said reducing gas atmosphere comprises carbon monoxide. 12.The process of either claim 1 or 2, wherein said torrefaction reactionis carried out with a reactant comprising hydrogen or ammonia.
 13. Theprocess of either claim 1 or 2, wherein said biomass feedstock isselected from the group consisting of, wood, paper, crops, animal andplant fats, biological waste, algae and mixture thereof.
 14. The processof claim 1, wherein said torrefaction reaction conditions includes atemperature ranging from 180° C. to 350° C., a pressure ranging from 0.1psia to 500 psia, and a residence time ranging from 1 min to 24 hours.15. A pyrolysis oil produced by a method according to claim
 1. 16. Apyrolysis oil produced by a method according to claim 2.